Objects of type
system_clock represent wall clock time from the system-wide
realtime clock
. Objects of type
sys_time<Duration> measure time since
1970-01-01 00:00:00 UTC excluding leap seconds
. This measure is commonly referred to as
Unix time. This measure facilitates an efficient mapping between
sys_time and calendar types (
[time.cal])
. [
Example 1:
sys_seconds{sys_days{1970y/January/1}}.time_since_epoch() is
0s. sys_seconds{sys_days{2000y/January/1}}.time_since_epoch() is
946'684'800s,
which is
10'957 * 86'400s. —
end example]